1. Field of the Invention
The present invention relates to torque converters, and more particularly to torque converters of a coreless type in which all of the three major elements (viz., pump impeller, turbine runner and stator) are coreless.
2. Description of the Prior art
In order to clarify the task of the present invention, one conventional coreless torque converter will be outlined with reference to FIG. 4 of the accompanying drawings, which converter is shown in SAE Paper 861213 and named as "Three Member Two Stage Type".
As shown in the drawing, the coreless torque converter comprises a pump impeller 100, a turbine runner 102 and a stator 104, which are the three major elements of the converter. These major elements 100, 102 and 104 have no cores at their blades. The torque converter of this coreless type can have two or three times of torque receiving capacity as compared with the common cored torque converter.
However, due to its inherent construction, the coreless torque converter has such a drawback that, since the blades of the pump impeller 100 and turbine runner 102 are formed with inwardly projected angular portions 100a and 102a to match in shape with the stator 104, the installation rigidity of the blades is relatively low and thus the characteristic frequency of each blade is low. Accordingly, during operation of the converter, such blades tend to vibrate due to vibration transmission from the engine and surge pressure by operating fluid running in the converter, which causes an undesired stress concentration at recessed parts 100b and 102b of the blades. In fact, when such stress becomes severe, crack may appear.